Determining the relationship between weeds and the wheat stem sawflies (Hymenoptera: Cephidae)'in wheat fields of Southeastern Anatolia

Wild mustard (Sinapis arvensis L.) is a cosmopolitan weed infesting roadsides, bare lands, agricultural fields, and pastures globally. It serves as a host for numerous insect pests and diseases. Wheat stem sawflies, i.e., Cephus pygmeus (L.) and Trachelus tabidus (F.) (Hymenoptera: Cephidae) exhibit higher density in the fields infested with wild mustard (either within field or on the field edges). This study investigated the relationship between wild mustard and sawflies' infestation in wheat fields of Diyarbakir and Sanliurfa provinces (southeastern Anatolia region) in Turkey. Wheat fields with high- and no- wild mustard infestation (5 from each province) were selected. These fields were subsequently divided into 30 × 30 m grids, and sampling was conducted in 40 grids. Sweep net and quadrate (0.25 m2) sampling methods were used to record the densities of sawflies and wild mustard, respectively in each grid. The collected data were analyzed by linear regression to observe the relationship between wheat stem sawflies and wild mustard infestation. Similarly, the differences between surveyed fields, provinces and wheat types were analyzed by analysis of variance. A total of 34 weed species belonging to 15 families were recorded from field edges and within fields during two years (2021, 2022). Wild mustard was the most common and abundant weed species recorded during the study. In addition, the other commonly observed species in the study fields were Avena fatua L. (wild oats), Hordeum spontaneum K. Koch (wild barley), and Rananculus arvensis L. (field buttercup). It was determined that the wheat stem sawflies emerged from the beginning of April, fed on wild mustard plants, and established dense population was on this weed. The density of wheat stem sawflies was higher in weed-infested fields (4.17 adults/grid) during 2021, whereas higher density of the sawflies was recorded in weed-free fields (5.33 adults/grid) during 2022. The results revealed that wild mustard plays a significant role in increasing the density of wheat stem sawflies in wheat fields of the region. Therefore, management strategies involving the management of wild mustard should be adopted to reduce the infestation of wheat stem sawflies in the region.